You're certainly not going to increase the population when eager would-be mothers die of complications from trying to carry a nonviable fetus to term/miscarriage. This is the reality of "late term abortion" the cultists love to harp on. Their great bogeyman is actually a straw man.

You're also not going to increase the population by discouraging IVF while the economic treadmill keeps on pushing people to put off kids.

As far as what they might argue? They will certainly argue anything, but it's never in good faith. Any lofty values they invoke to defend one policy will immediately vanish when they're asked to apply them to a contradictory policy. And like the import taxes, or the spectacle deportations, or the cries about the debt, we certainly could have a group of well reasoned national policies that would encourage having kids. But one or two policies seemingly picked for their mechanics of hurting people is most certainly not that kind of constructive approach.